A further massive transfer of Bastarnae was carried out by emperor Diocletian ( ruled 284-305 ) after he and his colleague Galerius defeated a coalition of Bastarnae and Carpi in 299.

Galerius was reinforced, probably in the spring of 298, by a new contingent collected from the Empire's Danubian holdings.

Diocletian believed that Romanus of Caesarea was arrogant, and he left the city for Nicomedia in the winter, accompanied by Galerius.

In 293, feeling more focus was needed on both civic and military problems, Diocletian, with Maximian's consent, expanded the imperial college by appointing two Caesars ( one responsible to each Augustus ) — Galerius and Constantius Chlorus.

After suffering a defeat by the Persians in 296, Galerius crushed Narseh in 298 — reversing a series of Roman defeats throughout the century — capturing members of the imperial household and a substantial amount of booty and gaining a highly favourable peace treaty, which secured peace between the two powers for a generation.

When Constantius died in 306, Galerius promoted Severus to Augustus while Constantine the Great was proclaimed Augustus to succeed his father Constantius, by his father's troops.

The country was fairly productive, especially after the great forests had been cleared by Probus and Galerius.

Constantine I, age 26, is declared Augustus ( emperor ) by his troops and awaits recognition by Emperor Galerius.

* Constantine is made a Caesar by Galerius and returns to Britain.

* Emperor Jovian negotiates a disastrous peace with Persia, surrendering four of the five Roman provinces gained by Caesar Galerius in 298, and the cities Nisibis and Singara ( Mesopotamia ).

But whereas Constantine's claim was recognized by Galerius, ruler of the Eastern provinces and the senior emperor in the empire, Maxentius was treated as a usurper.

Instituted by Diocletian, it was avidly pursued by Galerius who noticed that Constantius was well disposed towards the Christians, and saw it as a method of advancing his career prospects with the aging Diocletian.

Although prior to 303 there appeared to be tacit agreement between the Tetrarchs that Constantius ’ s son, Constantine and Maximian ’ s son Maxentius were to be promoted to the rank of Caesar once Diocletian and Maximian had resigned the purple, by the end of 304 Galerius had convinced Diocletian ( who in turn convinced Maximian ) to appoint Galerius ’ s nominees Severus and Maximinus Daia as Caesars.

He was trusted enough by Galerius that in 307 he was sent as an envoy to Maxentius in Italy to attempt to reach some agreement about his illegitimate status.

Their marriage was the occasion for the jointly-issued " Edict of Milan " that reissued Galerius ' previous edict allowing Christianity to be professed in the Empire, with additional dispositions that restored confiscated properties to Christian congregations and exempted Christian clergy from municipal civic duties. The redaction of the edict as reproduced by Lactantius-who follows the text affixed by Licinius in Nicomedia on June 14 313, after Maximinus ' defeat-uses a neutral language, expressing a will to propitiate " any Divinity whatsoever in the seat of the heavens ".

Maximinus has a bad name in Christian annals, as having renewed persecution after the publication of the toleration edict of Galerius ( see Edict of Toleration by Galerius ), acting outwardly as responding to the demands of various urban authorities asking for the expelling of Christians.

Eventually, on the eve of his clash with Licinius, he accepted Galerius ' edict ; after being defeated by Licinius, shortly before his death at Tarsus, he eventually issued an edict of tolerance on his own, granting Christians the rights of assembling, of building churches, and the restoration of their confiscated properties.

When Constantius died in 306, his son Constantine was crowned emperor on July 25 and subsequently accepted by Galerius into the tetrarchy as Caesar.

Maxentius refrained from using the titles Augustus or Caesar at first and styled himself princeps invictus ( Undefeated Prince ), in the hope of obtaining recognition of his reign by the senior emperor Galerius.

Diocletian delegated further on 1 March 293, appointing Galerius and Constantius as Caesars, junior co-emperors.

In the spring of 293, in either Philippopolis ( Plovdiv, Bulgaria ) or Sirmium, Diocletian would do the same for Galerius, husband to Diocletian's daughter Valeria, and perhaps Diocletian's praetorian prefect.

Galerius and Constantius would become Augusti after Diocletian and Maximian's departure.

Diocletian spent the spring of 293 traveling with Galerius from Sirmium ( Sremska Mitrovica, Serbia ) to Byzantium ( Istanbul, Turkey ).

Afterwards, during 299 and 302, as Diocletian was then residing in the East, it was Galerius ' turn to campaign victoriously on the Danube.

In a public ceremony at Antioch, the official version of events was clear: Galerius was responsible for the defeat ; Diocletian was not.

Diocletian publicly humiliated Galerius, forcing him to walk for a mile at the head of the Imperial caravan, still clad in the purple robes of the Emperor.

Diocletian and Galerius ' magister memoriae ( secretary ) Sicorius Probus were sent to Narseh to present terms.

At the conclusion of the peace, Diocletian and Galerius returned to Syrian Antioch.

Diocletian was conservative in matters of religion, a man faithful to the traditional Roman pantheon and understanding of demands for religious purification, but Eusebius, Lactantius and Constantine state that it was Galerius, not Diocletian, who was the prime supporter of the purge, and its greatest beneficiary.

Galerius, even more devoted and passionate than Diocletian, saw political advantage in the politics of persecution.

According to Lactantius, Diocletian and Galerius entered into an argument over imperial policy towards Christians while wintering at Nicomedia in 302.

Diocletian argued that forbidding Christians from the bureaucracy and military would be sufficient to appease the gods, but Galerius pushed for extermination.

Galerius convinced Diocletian that the culprits were Christians, conspirators who had plotted with the eunuchs of the palace.

Galerius assumed the consular fasces in 308 with Diocletian as his colleague.

In the autumn of 308, Galerius again conferred with Diocletian at Carnuntum ( Petronell-Carnuntum, Austria ).

Diocletian and Maximian were both present on 11 November 308, to see Galerius appoint Licinius to be Augustus in place of Severus, who had died at the hands of Maxentius.

Compendium extract: Diocletian to the Death of Galerius: 284 – 311

Afterward, the persecutions under Diocletian and Galerius directed his attention to the martyrs of his own time and the past, and this led him to the history of the whole Church and finally to the history of the world, which, to him, was only a preparation for ecclesiastical history.

The point of the work is to describe the deaths of the persecutors of Christians: Nero, Domitian, Decius, Valerian, Aurelian, and the contemporaries of Lactantius himself, Diocletian, Maximian, Galerius, and Maximinus.

* 293 – Roman Emperors Diocletian and Maximian appoint Galerius as Caesar to Diocletian, beginning the period of four rulers known as the Tetrarchy.

It was expected that Maxentius would remain within Rome and endure a siege, as he already had successfully employed this strategy during the invasions of Severus and Galerius.